Gamma cameras according to the prior art are provided with collimators comprised of several inches of lead, having a plurality of usually parallel channels therethrough, thus limiting the field of view to parallel gamma rays or gamma rays emitted over a very small angular cone.
However, in certain instances, according to the prior art, the channels through the lead collimator are conically aligned so that rays emitted from a relatively close point source may be imaged throughout the entire face of the scintillating crystal. This is shown, for example, in U.S. Pat. No. 4,068,126 issued Jan. 10, 1978 to D. T. Wilson.
Gamma cameras, as previously stated, are utilized to image organs which have taken up radioactive material. Another very common form of radiographic study used in the prior art is called an uptake. In an uptake, radioactive material is given to the patient and is taken up by a selected organ. The amount of radioactive material taken up may be indicative of a disease process. Thus, at a predetermined time after the patient has taken the radioactive material, according to the prior art, the organ is exposed to a single scintillation detector which merely counts the total number of gamma rays produced. The total number of counts received by the scanner indicates the amount of radioactive uptake.
Although gamma cameras are provided with counters, they cannot be practically employed for uptakes since the amount of time required for the uptake study would be very large, due to the fact that the gamma camera cannot count every gamma ray or gamma particle reaching the scintillating material, as previously described. Furthermore, at high count rates the counts registered by a gamma camera are not proportional to the actual counts received.
I have discovered that gamma cameras may be very successfully employed for uptake studies, such as thyroid studies, by masking or shielding off the greater portion of the gamma camera and providing the remaining central portion with a generally cylindrical open collimator. Most conveniently this flat field collimator may be provided as an adapter for conical collimators supporting pinholes which are also utilized by gamma cameras.
Additional collimators can also be provided according to my invention. For example, another adapter collimator interfitting to the conical pinhole supporting collimator, may be a restricted field lead cylinder having a plurality of parallel channels therethrough. This collimator may be used for small organ gamma studies and due to the great length of the passageways increases the gamma camera's resolutioin as disclosed in U.S. Pat. No. 4,118,632, issued Oct. 3, 1978 to Heribert Luig.
In another embodiment of the invention the adapter may be provided with long channels which diverge from the organ to the scintillating crystal to provide an image magnification.
In another alternative embodiment the flat field straight bore collimator may be a separate collimator rather than an adapter for use with a pinhole collimator.